1. Field of the Invention
The invention relates to a skag for a ski. More particularly, the invention relates to a skag that includes dual parallel rails and/or dual parallel keels, so as to provide improved maneuverability.
2. Description of Related Art
Skis and their use on vehicles are well known. FIG. 1 shows a conventional vehicle 1 (a snowmobile) with a ski 2 thereon. Conventional skis consist of a strip of material that is usually smooth or nearly smooth along its bottom surface. Conventional skis are used to support vehicles or persons on snow, ice, and similar terrain.
It is often desirable to make skis of materials that are relatively light, i.e. to reduce the weight of a vehicle, and/or flexible, i.e. to enable the ski to temporarily flex or deform instead of breaking when it is subjected to stress.
However, the terrain in which skis conventionally are used is often rough, and may subject the skis to considerable wear. Furthermore, even relatively smooth layers of snow, ice, etc. can be highly abrasive under certain conditions. Skis made from many materials that are light and/or flexible may wear out and/or break after a relatively short time.
To address this problem, a more durable material may be attached to the lower surface of the skis. Sometimes referred to as “rails” or “wear strips”, they are adapted to resist wear, thereby increasing the usable life of the ski. In some cases, rather than being disposed directly on the ski, the rails may be disposed on a carrier platform, such as a strip or bar of metal that conforms to and is connected to the bottom surface of the ski.
As a further matter, skis without rails or some similar structure have limited ability to “grip” or “bite” snow or ice. This is of special concern when maneuvering the vehicle to which the ski is connected, i.e. when turning. Greater maneuverability may be desirable, especially at high speeds.
The previously described rails or wear strips may provide additional maneuverability beyond that possible with an otherwise smooth ski, in addition to increasing durability. By projecting downward into and/or against the snow or ice, the rails provide increased grip, and therefore improved maneuverability.
In addition, it is possible to shape the rail or a portion thereof so as to form a longitudinal keel shape, such as a wedge or a blade. Alternatively, a keel can be formed separately and mounted to a ski, without necessarily including a rail. The keel functions in a manner similar to the rail with regard to maneuverability, i.e. it cuts into the snow, ice, or other terrain on which the ski rests, providing improved bite or grip that enhances the performance, stability, and maneuverability of the ski.
In common use, the term “skag” sometimes is used to describe such a keel, and sometimes is used to describe a full assembly with such a keel that is attached to a ski. As used herein, the term “skag” is used with the latter definition, that is, a skag is a structure disposed on the lower side of a ski, which includes rails and/or a keel as described above.
A skag typically is attached to the bottom surface 3 of a conventional ski, as shown in FIG. 1.
Conventional skags have several limitations.
First, because it cuts into the underlying surface, the keel of a conventional skag often leaves behind a trail or groove. If a second vehicle with a conventional skag later follows the same path, the skag on that second vehicle may follow the track from the first vehicle, thereby aligning the second vehicle's ski with the path followed by the first vehicle. Later vehicles also may follow the track, making it deeper and more pronounced.
As a result, the second and later vehicles tend to follow closely the path of the first vehicle, and resist efforts to steer out of that path. In addition, the second and later vehicles tend to shift, sometimes abruptly, to align themselves with the path of the first vehicle if that path is crossed. These phenomena are sometimes collectively referred to as “groove follow”. The former also may be referred to as “tracking”, while the latter may be referred to as “darting”. Both phenomena may affect the maneuverability of the second and later vehicles.
Although it is possible to overcome darting and tracking by deliberately steering a vehicle out of the path of preceding vehicles, or by avoiding such earlier paths altogether, such solutions may not always be desirable.
For example, snowmobiles, which have used skis with conventional skags, are often used on dedicated snowmobile trails. Trails are not always sufficiently spacious to make it possible for vehicle operators to avoid the grooves left by previous vehicles. This is especially true in popular trails, and in areas of heavy traffic on a trail.
Furthermore, even if it is possible to make a special effort to avoid grooves from previous vehicles, it may be difficult or undesirable to do so.
Attempts to overcome this problem have been made. For example, in U.S. Pat. No. 5,344,168 to Olson et al., a generally flat bar is employed to disrupt existing skag grooves in an effort to avoid tracking and darting. However, the addition of this bar increases the drag on the ski, since in order for the bar to function it must dig into and break up the snow or ice in order to fill in the groove. Furthermore, the bar may not be effective in disrupting grooves in hard packed snow, or in wet snow that has frozen into ice.
Another feature of conventional skags that might be improved is the ability to maneuver. Although conventional skags provide increased maneuverability over skis lacking such structures, still greater maneuverability may be desired, especially at high speeds.
The ability to maneuver with a ski with a skag thereon depends in part upon the size of the skag's rail and/or keel. As the skag is made longer, it provides greater grip or “bite” into the underlying surface, thereby allowing more force to be applied when turning.
In addition, increasing the length of a skag reduces the total weight per unit length that must be borne thereby, assuming vehicle weight is not also increased when the skag is lengthened. This may contribute to reduced wear on the skag.
However, a long longitudinal skag also has disadvantages. For example, although the skag provides maneuverability, the skag itself must be made to turn against the snow or ice surrounding it on both sides. Thus, as the skag is lengthened, more force is required to turn it.
In addition, a ski on a vehicle that is turning typically follows a curved path. As the length of a conventional straight skag increases, the ends of the skag deviate by a greater distance from that curved path. A long straight skag following a curved path may cause the vehicle to turn roughly, or in “stutters”.
In addition, turning a ski with a skag thereon puts stress on the skag. As the skag length increases, the stress increases. At some point this can contribute to greater wear, and/or damage to the skag as a whole, its component parts, and/or the ski to which it is attached. For example, the increased stresses experienced by long skags may cause the skag to eventually become worn to the point that it must be replaced. The increased stresses for a long ski skag may also result in the failure of the ski skag, i.e. by the keel separating from the rail, by the rail separating from the carrier platform, by the skag or some portion thereof bending into an S-curve or otherwise deforming, etc. Because stress increases with increasing skag length, a longer ski skag is proportionally weaker than a shorter one, assuming they are made from similar materials using similar methods of construction.
Thus, although it is in some respects desirable to increase the total length of the skag, other factors limit the utility and durability of long conventional skag. For this reason, increasing the length of a conventional skag beyond a certain point does not provide further improvements in maneuverability for a vehicle equipped with a conventional skag.